Network configuration audit

ABSTRACT

A cell planning tool capable of determining the correctness of stored parameters regarding a cell site configuration, e.g., regarding the height of an antenna section or the output power. The correctness of the parameters is determined by importing a number of in-situ signal strength-measurements from measuring points located within the coverage area of said cell site and predicting the signal-strength at each of said measuring points, using said stored parameters. Thereafter, the difference between the imported and the corresponding predicted signal-strength is calculated for each measuring point, and a value indicating the correctness of the stored parameters is estimated, based on said calculated signal-strength differences.

TECHNICAL FIELD

The present invention relates to a method in a cell planning tool, andto a cell planning tool, capable of determining the correctness ofstored parameters associated with a cell site.

BACKGROUND

An operator of a mobile communication network, e.g. according to the GSM(Global System for Mobile communication) or UMTS (Universal MobileTelecommunication System), is normally assisted by a cell planning toolin designing, planning and optimizing the network. A cellular mobilecommunication network comprises a large number of cell sites, each cellsite comprising an antenna arrangement configured to provide the desiredcell coverage. FIG. 1 a is a perspective view illustrating an exemplaryconventional antenna 12 of a cell site, and FIG. 1 b is a top view ofsaid antenna 12, schematically illustrating three antenna sectors, 14 a,14 b, 14 c, providing coverage in three cells, and the sectors may havedifferent transmission frequencies. The antenna is mounted on the cellsite with a certain configuration indicated by parameters regarding e.g.the height, the transmitting signal output power, antenna type and thedirection, and parameters describing the network configuration ispreferably stored in a cell planning tool of the operator.

A conventional cell planning tool is normally provided with severalalgorithms using the above-described stored parameters to calculate thenetwork performance, and the algorithms may include e.g. trafficdistribution algorithms and Monte Carlo simulators. The cell planningtool uses map data as input to the algorithms, together with variousnetwork configuration data regarding e.g. the base station hardware andother auxiliary hardware, such as feeders and combiners. The output fromthe cell planning tool comprises network performance information, suchas e.g. an estimation of the cell site coverage area and the predictedsignal strength in different locations within the coverage area, and theoperator may use this information for cell planning in order to plan andoptimize the network for achieving certain network key performanceindicator targets.

Obviously, the parameters stored in the cell planning tool regardinge.g. the antenna configuration, such as the height and the angularorientation of the antenna, will always deviate to some extent from theactual height and angular orientation of the antenna, but preferably thedeviations will be negligible. If the deviation of the networkconfiguration parameters stored in the cell planning tool from theactual deployed network configuration parameters is negligible, theresulting errors in the output from the cell planning tool will besmall. However, larger errors may sometimes occur, e.g. if the antennaelement is not mounted on the intended height or with the intendedangular orientation.

Thus, to avoid any detrimental effect on the network performance causedby large deviations, manual inspections and audits of the cell site andthe antenna must be performed regularly in order to check e.g. that themounting of the antenna section corresponds to the stored parametersregarding the height and angular orientation of the antenna, but suchmanual audits are very costly.

Therefore, it still presents a problem to correlate stored parametersassociated with a cell site configuration in a cell planning tool withthe actual deployed cell site configuration in a cost-efficient way,avoiding manual audits of the cell site.

SUMMARY

An object of the present invention is to address the problem outlinedabove, and this object and others are achieved by the method in a cellplanning tool, and the cell planning tool, according to the appendedclaims.

According to a first aspect, the invention provides a method in a cellplanning tool of determining the correctness of stored parametersassociated with a cell site configuration, and the method comprises thefollowing steps:

-   -   Importing in-situ signal strength-measurements, SSmeasure, from        measuring points located within the coverage area of said cell        site;    -   Predicting the signal-strength, SSpredict, at each of said        measuring points using said stored parameters associated with        the cell site configuration;    -   Calculating the signal strength-difference between the imported        in-situ signal strength-measurements and the corresponding        predicted signal-strength for each measuring point;    -   Estimating a value indicating the correctness of the stored        parameters based of said calculated signal strength-differences.

Thereby, the number of manual network configuration audits of a cellsite can be reduced considerably, since the operator will be able todetermine the correctness of parameters stored in the cell planning toolwithout performing any manual network configuration audit. Only if thisdetermination of the correctness reveals a deviation of the storedparameters from the actual parameters that is not negligible, a manualnetwork configuration audit may have to be performed.

The above step of estimating a value indicating the correctness of thestored parameters may comprise the following sub-steps:

-   -   Dividing the coverage area into a selected number of segments;    -   Calculating a first average value, Δaver, for each segment        separately, corresponding to the average of the calculated        signal strength-differences of the segment;    -   Calculating a first standard deviation value, σ1, for each        segment separately, corresponding to the standard deviation of        said calculated signal strength differences of the segment;    -   Calculating a second average value, σ1aver, corresponding to the        average of said calculated first standard deviation values; and    -   Calculating a second standard deviation value, σ2, corresponding        to the standard deviation of said calculated first standard        deviation values.

According to a second aspect, the invention relates to a cell planningtool for a network configuration, provided with an arrangement fordetermining the correctness of stored parameters associated with a cellsite configuration, and the arrangement comprises a receiving unitadapted to import in-situ signal strength-measurements, SSmeasure, frommeasuring points located within the coverage area of said cell site, anda processing unit adapted to:

-   -   Predict the signal-strength, SSpredict, at each of said        measuring points using said stored parameters associated with        the cell site configuration;    -   Calculate the signal strength-difference between imported        in-situ signal strength-measurements and the corresponding        predicted signal-strength for each measuring point;    -   Estimate a value indicating the correctness of the stored        parameters based of said calculated signal strength-differences.

The processing unit may be further adapted to:

-   -   Divide the coverage area into a selected number of segments;    -   Calculate a first average value, Δaver, for each segment        separately, corresponding to the average of the calculated        signal strength-differences for the segment;    -   Calculate a first standard deviation value, σ1, for each segment        separately, corresponding to the standard deviation of said        calculated signal strength differences for the segment;    -   Calculate a second average value, σ1aver, corresponding to the        average of said calculated first standard deviation values;    -   Calculate a second standard deviation value, σ2, corresponding        to the standard deviation of said calculated first standard        deviation values.

The estimated value indicating the correctness may correspond to saidsecond standard deviation value, σ2, and the calculated second averagevalue σ1aver may indicate the correctness of the output signal power.The estimated value indicating the correctness may correspond to saidfirst standard deviation value, σ1, if the number of segments is onlyone.

The segments may have a similar size, and extreme in-situsignal-strength measurement may be excluded in the calculations.Further, said segments may cover only a part of said coverage area,corresponding to substantially 90 degrees of the coverage area in theangular direction.

The number of segments may have a default value, e.g. nine, and thenumber of segments may be settable by the operator. Alternatively, thenumber of segments may be calculated automatically by the cell planningtool, depending on the number of imported in-situ signal-strengthmeasurements.

The stored parameters may comprise e.g. the output signal power, theheight, and the angular orientation of each of the antenna-sections ofthe cell site.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail and withreference to the accompanying drawings, in which:

FIG. 1 a is a perspective view of an exemplary antenna configuration ofa cell site;

FIG. 1 b is a top view of said antenna, illustrating the three sectorsof the antenna;

FIG. 2 is a top view of a part of the coverage area divided into ninesegments, according to one embodiment of this invention;

FIG. 3 is a flow diagram of an exemplary embodiment of the methodaccording to the invention, and

FIG. 4 is a block diagram illustrating a cell planning tool providedwith an arrangement according this invention.

DETAILED DESCRIPTION

In the following description, specific details are set forth, such as aparticular architecture and sequences of steps in order to provide athorough understanding of the present invention. However, it is apparentto a person skilled in the art that the present invention may bepractised in other embodiments that may depart from these specificdetails.

Moreover, it is apparent that the described functions may be implementedusing software functioning in conjunction with a programmedmicroprocessor or a general purpose computer, and/or using anapplication-specific integrated circuit. Where the invention isdescribed in the form of a method, the invention may also be embodied ina computer program product, as well as in a system comprising a computerprocessor and a memory, wherein the memory is encoded with one or moreprograms that may perform the described functions.

A network operator regularly performs manual measurements relating tothe cell site by collecting measurement data, e.g. using a vehicleequipped with an antenna travelling within the coverage area of the cellsite and measuring the signal strength at different positions, andstoring the collected signal strength values, together with the positionof the measuring points. This invention determines the correctness ofthe stored parameters in a cell planning tool by an added functionalitycapable of importing such measurements collected by the operatorregarding the signal strength at different positions within the coveragearea of the cell site, and comparing these measurements with thepredicted signal strength values in said positions, the predictionperformed by the cell planning tool, based on said stored parameters.

According to this invention, a value indicating the correctness of thestored cell site configuration-parameters in the cell planning tool isestimated based on calculated differences between the in-situ measuredsignal strength and the predicted signal strength in a suitable numberof measuring points within the coverage area of the cell site. Theestimation is performed by a suitable statistical procedure, e.g. bysimply determining the average value of the calculated differencesbetween the measured signal strength and the predicted signal strengthin the measuring points, or by a more complex mathematical process,which may include dividing the coverage area into a suitable number ofsegments.

Thereafter, this estimated value indicating the correctness may e.g. becompared to a predetermined threshold value in order to determinewhether the deviation is acceptable. If not, the operator has the optionto e.g. adjust the antenna transmission output power, or to perform amanual inspection of the cell site in order obtain more correctparameters to be stored in the cell planning tool. The cell siteconfiguration parameters stored in the cell planning tool may comprisethe output signal power of each of the antenna-sections of the cellsite, the height of each of the antenna-sections of the cell site or theangular orientation of each of the antenna sections of the cell site.

The invention will now be described with reference to FIG. 2, which is atop view schematically illustrating an antenna segment 14 of a cellsite, and a part of the coverage area 22 divided into nine segments 26.Measuring values regarding the actual signal strength and the positionhave been collected by the operator in a suitable number of measuringpoints 28, by a person or a vehicle provided with measuring equipmentand travelling a path 24. According to this invention, a cell planningtool imports the collected signal strength measurements, as well as thecorresponding positions, and identifies the serving cell for eachmeasurement in order to determine the measurements associated with aspecific cell site. Next, the cell planning tool predicts the signalstrength value in the measuring points, and calculates the difference insignal strength between the imported values and said predicted values,SSmeas−SSpred=Δ for each measuring point. Thereafter, an estimation ofthe correctness of the stored parameters is performed, based of saidcalculated signal strength-differences.

According to a first embodiment of the invention, the coverage area isdivided into a suitable number of segments 26, normally at least fourand less than twenty, depending e.g. on the number of imported in-situmeasurements associated with a certain cell site. A default value of thenumber of segments is preferably stored in the cell planning tool, andthis default value may e.g. be around nine, in order to achievesatisfactory accuracy.

According to further exemplary embodiments, the number of segments issettable by the operator, or calculated by the cell planning tool,depending e.g. on the number of imported signal strength measurements.Further, in the illustrated embodiment, only a part of the coverage areais used, corresponding to an area within ±45 degrees from the servingantenna. However, any other suitable portion of the coverage area may beused, or the entire coverage area, and the coverage area may be dividedinto any suitable number of segments, or into only one segment, e.g.depending on the number of imported measurements an on the requiredcorrectness and speed of the calculations.

According to this first embodiment, a first average value, Δaver, iscalculated for each individual segment, representing the average signalstrength difference for the measuring points for the segment, but somevalues may be excluded, e.g. extreme values. Thereafter, a firststandard deviation value, σ1, is calculated for each of the segments,representing the standard deviation of the signal strength differencesin the segment. Next, a second average value, σ1aver, is calculated,representing the average of said calculated first standard deviationvalues. Based on this second average value, a second standard deviationvalue, σ2, is calculated, representing the standard deviation of saidcalculated first standard deviation values. However, a segmentcontaining very few measuring points may be excluded from thecalculation.

Said second standard deviation value, σ2, will indicate specifically thecorrectness of the stored cell site configuration parameters, and alarge standard deviation value will indicate a larger deviation, and asmaller standard deviation value will indicate a smaller deviation, andmore correct stored parameters.

The second average value, σ1aver, will indicate the correctness of thestored output signal power-parameter, and a large second average valuewill indicate a larger deviation in the stored output signal power.

According to a further embodiment, said first standard deviation value,σ1, representing the standard deviation of the signal strengthdifferences, will be used as an indication of the correctness of thestored parameters, in case the coverage area is divided into only onesegment. Alternatively, it is possible to use said first calculatedaverage value, Δaver, as an indication of the correctness of the storedparameters, but the standard deviation, σ1, will normally give a betterestimation.

The suitable number of segments depends on the number of measuringpoints, and fewer segments will result in a faster calculation, while alarger number of segments will increase the accuracy.

FIG. 3 is a flow chart illustrating an exemplary embodiment of thisinvention, in which a number of signal strength measurements areimported, and the coverage area is divided into a selected number ofsegments. In step 300, a number of collected and stored in-situ signalstrength-measurements, SSmeasure, from measuring points located withinthe coverage area of said cell site, are imported, together with theposition of each measuring point. Thereafter, a predictedsignal-strength, SSpredict, is calculated for each of said measuringpoints, in step 305, using said stored parameters associated with thecell site configuration. In step 310, the signal strength-differencebetween the imported in-situ signal strength-measurements and thecorresponding predicted signal-strength is calculated for each measuringpoint, and in step 315, the coverage area is divided into a selectednumber of segments having approximately similar size, each segmentincluding a suitable number of measuring points. In step 320, a firstaverage value, Δaver, is calculated for each segment separately,corresponding to the average of the calculated signalstrength-differences for the segment, and a first standard deviationvalue, σ1 is calculated for each segment separately, in step 325,corresponding to the standard deviation of the signal strengthdifferences for the segment. Next, in step 330, a second average value,σ1aver, is calculated, corresponding to the average value of thestandard deviations of all the segments, and a second standard deviationvalue is calculated, in step 335, corresponding to the standarddeviation of the first standard deviation values. This calculated secondstandard deviation value, σ2, indicates the correctness of the storedparameters, and a large standard deviation value will indicate a largerdeviation, i.e. a larger error in the stored network configurationparameters, while the calculated second average value, σ1aver, indicatesthe correctness of the output signal power.

FIG. 4 is a block diagram illustrating a cell planning tool according toan exemplary embodiment of this invention, comprising a cell planningtool 40 provided with an arrangement 42 for determining the correctnessof stored parameters associated with a cell site configuration. Thisarrangement comprises a receiving unit 44 adapted to import in-situsignal strength-measurements, SSmeasure, and the correspondingpositions, from a number of measuring points located within the coveragearea of said cell site, and a processing unit 46 adapted to predict thesignal-strength, SSpredict, at each of said measuring points usingstored parameters associated with the cell site configuration.

According to a first embodiment, the processing unit 46 is adapted todivide the coverage area into a number of segments, each segmentincluding a suitable number of measuring points. The processing unit isfurther adapted to calculate a first average value, Δaver, for eachsegment separately, representing the average of the signalstrength-difference in the measuring points for the segment. Next, afirst standard deviation value, σ1, is calculated for each segmentseparately, representing the standard deviation of the signal strengthdifferences for the segment, and, thereafter, a second average value,σ1aver, is calculated, representing the average of said first standarddeviation values. Finally, a second standard deviation value σ2, iscalculated, representing the standard deviation of said first calculatedstandard deviation values. According to a first embodiment of theinvention, the processing unit is adapted to use this second standarddeviation value, σ2, as an indication of the correctness of the storedparameters in the cell planning tool.

According to a further embodiment, the processing unit 46 is adapted touse said second calculated average value, σ1aver, as an indication ofthe correctness of the stored output power-parameter.

According to a second embodiment, the processing unit 46 is adapted touse said calculated first standard deviation value, σ1, of the signalstrength differences as an indication of the correctness of the storedparameters, in case the coverage are is divided into only one segment,or alternatively, said calculated first average value, Δaver, of thesignal strength differences in each measuring point.

According to another embodiment of the cell planning tool, a defaultvalue of the number of segments is stored, and a suitable default valueof the number of segments may e.g. be around nine, in order to achieve asatisfactory accuracy. According to a further exemplary embodiment, thenumber of segments is settable by the operator. According to anotherembodiment, the processing unit is adapted to divide the coverage areainto a suitable number of segments, normally at least four and less thantwenty, depending e.g. on the number of imported measurements associatedwith a certain cell site.

Further, according to an exemplary embodiment, the processing unit isadapted to use only a part of the coverage area, corresponding to anarea within ±45 degrees from the serving antenna. However, any othersuitable portion of the coverage area may be used, or the entirecoverage area, and the coverage area may be divided into any suitablenumber of segments, or into only one segment, e.g. depending on thenumber of imported measurements.

This invention may e.g. be implemented as an added functionality in anexisting cell planning tool, enabling the operator to determine thecorrectness of the stored parameters without a manual networkconfiguration audit. Only if the determination of the correctness,according to this invention, reveals a deviation of the storedparameters from the actual parameters that is not negligible, a manualnetwork configuration audit may have to be performed. Thereby, the needof manual network configuration audits will be reduced considerably.

While the invention has been described with reference to specificexemplary embodiments, the description is in general only intended toillustrate the inventive concept and should not be taken as limiting thescope of the invention.

1. A method in a cell planning tool of determining the correctness ofstored parameters associated with a cell site configuration, comprisingthe steps of: Importing in-situ signal strength-measurements, SSmeasure,from measuring points located within the coverage area of said cellsite; Predicting the signal-strength, SSpredict, at each of saidmeasuring points using said stored parameters associated with the cellsite configuration; Calculating the signal strength-difference betweenthe imported in-situ signal strength-measurements and the correspondingpredicted signal-strength for each measuring point; Estimating a valueindicating the correctness of the stored parameters based of saidcalculated signal strength-differences.
 2. A method according to claim1, wherein said step of estimating a value indicating the correctness ofthe stored parameters comprises the sub-steps of: Dividing the coveragearea into a selected number of segments; Calculating a first averagevalue, Δaver, for each segment separately, corresponding to the averageof the calculated signal strength-differences of the segment;Calculating a first standard deviation value, σ1, for each segmentseparately, corresponding to the standard deviation of said calculatedsignal strength differences of the segment; Calculating a second averagevalue, σlaver, corresponding to the average of said calculated firststandard deviation values; Calculating a second standard deviationvalue, σ2, corresponding to the standard deviation of said calculatedfirst standard deviation values.
 3. A method according to claim 2,wherein the estimated value indicating the correctness corresponds tosaid second standard deviation value, σ2.
 4. A method according to claim2, wherein said calculated second average value σlaver indicates thecorrectness of the output signal power.
 5. A method according to claim2, wherein the estimated value indicating the correctness corresponds tosaid first standard deviation value, σ1, if the number of segments isonly one.
 6. A method according to claim 2, wherein the segments have asimilar size.
 7. A method according to claim 2, wherein extreme in-situsignal-strength measurement are excluded in the calculations.
 8. Amethod according to claim 2, wherein said segments covers only a part ofsaid coverage area, said part corresponding to substantially 90 degreesof the coverage area in the angular direction.
 9. A method according toclaim 2, wherein the number of segments has a default value.
 10. Amethod according to claim 9, wherein said default value of the number ofsegments is nine.
 11. A method according to claim 2, wherein the numberof segments is settable by the operator.
 12. A method according to claim2, wherein the number of segments is calculated automatically, dependingon the number of imported in-situ signal-strength measurements.
 13. Amethod according to claim 2, wherein one of the said stored parameterscomprises the output signal power of each of the antenna-sections of thecell site.
 14. A method according to claim 2, wherein one of the saidstored parameters comprises the height of each of the antenna-sectionsof the cell site.
 15. A method according to claim 2, wherein one of thesaid stored parameters comprises the angular orientation of each of theantenna sections of the cell site.
 16. Cell planning tool for a networkconfiguration, wherein the cell planning tool is provided with anarrangement for determining the correctness of stored parametersassociated with a cell site configuration, said arrangement comprising:A receiving unit to import in-situ signal strength-measurements,SSmeasure, from measuring points located within the coverage area ofsaid cell site; A processing unit to: a. Predict the signal-strength,SSpredict, at each of said measuring points using said stored parametersassociated with the cell site configuration; b. Calculate the signalstrength-difference between imported in-situ signalstrength-measurements and the corresponding predicted signal-strengthfor each measuring point; c. Estimate a value indicating the correctnessof the stored parameters based of said calculated signalstrength-differences.
 17. A cell planning tool according to claim 16,wherein said processing unit: divides the coverage area into a selectednumber of segments; calculates a first average value, Δaver, for eachsegment separately, corresponding to the average of the calculatedsignal strength-differences for the segment; calculates a first standarddeviation value, σ1, for each segment separately, corresponding to thestandard deviation of said calculated signal strength differences forthe segment; calculates a second average value, σaver, corresponding tothe average of said calculated first standard deviation values;calculates a second standard deviation value, σ2, corresponding to thestandard deviation of said calculated first standard deviation values.18. A cell planning tool according to claim 17, wherein the estimatedvalue, indicating the correctness of the stored parameters, correspondsto said second standard deviation value, σ2.
 19. A cell planning toolaccording to claim 17, wherein said second average value, σlaver,indicates the correctness of the output signal power.
 20. A cellplanning tool according to claim 17, wherein the estimated correctionvalue, indicating the correctness of the stored parameters, correspondsto said first standard deviation value, σ1, if the number of segments isonly one.
 21. A cell planning tool according to claim 17, wherein thesegments have a similar size.
 22. A cell planning tool according toclaim 17, wherein said segments covers a part of said coverage area,said part corresponding to substantially 90 degrees of the coverage areain the angular direction.
 23. A cell planning tool according to claim17, wherein the number of segments has a default value.
 24. A cellplanning tool according to claim 23, wherein said default value of thenumber of segments is nine.
 25. A cell planning tool according to claim17, wherein the number of segments is settable by the operator.
 26. Acell planning tool according to claim 17, wherein said processing unit(46) is further adapted to calculate the number of segments, dependingon the number of imported in-situ signal-strength measurements
 27. Acell planning tool according to claim 17, wherein one of said storedparameters comprises the output signal power of each of theantenna-sections of the cell site.
 28. A cell planning tool according toclaim 17, wherein one of the said stored parameters comprises the heightof each of the antenna-sections of the cell site.
 29. A cell planningtool according to claim 17, wherein one of the said stored parameterscomprises the angular orientation of each of the antenna sections of thecell site.